a. Field of the Invention
The present invention relates to shroud nozzles to be coupled to a ladle in a metal casting installation for shielding from contact with air the molten metal flowing out of the ladle into a tundish. Such nozzles are commonly referred to as ladle shrouds. In particular, it relates to a coupling device for holding a ladle shroud in casting position with respect to a collector nozzle jutting out of the bottom floor of a ladle without any external means. The present invention also concerns a ladle shroud to be used with such coupling device and concerns a metal casting installation comprising both ladle shroud and coupling device.
b. Description of the Related Art
In metal forming processes, metal melt is transferred from one metallurgical vessel to another, to a mould or to a tool. For example, as shown in FIG. 1a ladle (11) is filled with metal melt out of a furnace (not shown) and transferred to a tundish (10) through a ladle shroud (111) extending from the ladle to the interior of the tundish for protecting the molten metal from contact with air. The metal melt can then be cast through a pouring nozzle (101) from the tundish to a mould (100) for forming slabs, billets, beams or ingots. Flow of metal melt out of a metallurgic vessel is driven by gravity through a nozzle system (101, 111) located at the bottom of said vessel.
In particular, the ladle (11) is provided at the inner surface of its bottom floor with an inner nozzle (113). Said inner nozzle is aligned with a collector nozzle (112) jutting out of the outer surface of said bottom floor, and is separated therefrom by a gate (114), generally a sliding gate (linear or rotary), allowing the bringing of the inner nozzle in or out of fluid communication with the collector nozzle, to start or stop casting metal, respectively. In order to protect the molten metal from oxidation as it flows from the ladle to a tundish (10), a ladle shroud (111) is interposed between the collector nozzle and the top surface of the molten metal contained in the tundish, penetrating deep into the tundish. A ladle shroud is simply a long tube with a central bore, which inlet is suitable for snugly nesting the outer surface of the collector nozzle in a casting configuration wherein a seal Is formed between the outer surface of the collector nozzle (112) and the inner surface of the bore inlet orifice of the ladle shroud (111).
In practice, a ladle is brought to its casting position over a tundish or a mould from a furnace where it was filled with a new batch of molten metal, with the gate (114) in a closed configuration. During its trips from the furnace to the casting position and back, the ladle is not coupled to any ladle shroud because the latter is too long and juts out too dangerously to be travelling to and fro across a steel plant. Once the ladle is in its casting position, a robot (20) or other handling tool brings a ladle shroud (111) into casting configuration with the collector nozzle (112) snugly nested in the bore inlet of the ladle shroud (cf. FIGS. 1&2). In traditional casting installations, the robot (20) also maintains the ladle shroud in its casting configuration during the whole casting of the molten metal batch contained in the ladle. When the ladle is empty, the gate is closed and the robot retrieves the ladle shroud from the collector nozzle to allow the removal of the empty ladle (11) and replacement by another ladle filled with a new batch of molten metal. The robot (20) repeats the foregoing operations with the new ladle.
Emergencies may happen, with the gate not functioning properly, requiring the swift removal of the ladle from its casting position and emptying of its content of molten metal into an appropriate emergency waste area. If the ladle shroud is coupled to the collector nozzle of the ladle with the robot firmly gripping the former in its casting configuration, the emergency removal of the ladle will drag therewith both ladle shroud and robot, causing serious damages to the installation. Indeed, the robot cannot be dragged very far, and the ladle may be blocked halfway, casting molten metal in an inappropriate area of the workshop causing serious consequences and danger.
To prevent such accidents to occur, ladle shrouds comprising means for holding them in casting configuration without the need of a robot have been proposed in the art. This way, the swift removal of a ladle would certainly break the ladle shroud, but would not drag and be stopped by a bulky (and expensive) robot in its emergency removal run.
For example, JP09-2011657 proposes a nozzle provided with coupling means including a bayonet requiring the rotation of the nozzle about its longitudinal axis to block it in its casting configuration. Such rotation can become very difficult as soon as the slightest amount of metal melt flows into and jags the bayonet mechanism upon freezing. Alternatively, JP09-1008825 proposes a nozzle comprising two long pins on either side thereof suitable for being held in casting configuration by a moving bracket comprising complementary slots for receiving said pins. This mechanism requires much room at one side of the ladle to function and necessitates an excellent coordination between the loading of a ladle shroud nozzle onto the slots of the brackets, and the tilting of the latter in a clamping configuration.
It certainly remains a need in the art for ladle shrouds which can hold themselves in their casting configuration without the assistance of a robot or any other external assistance, which are simple and financially competitive, which require little coordination and with moving parts well away from the interface between inlet of the bore of the ladle shroud and the outer surface of the collector nozzle, to prevent jagging thereof by frozen metal. These and other advantages of the present invention are presented in the following sections.